This invention relates generally to a boom on a machine, and more particularly to a method and an apparatus for controlling the angular velocity of the boom on the machine.
Many machines, including, for example telehandlers, include booms. Generally an implement such as, for example, a bucket, fork tines or basket, is located at the end of the boom for manipulation by the operator. A typical boom can be extended over twenty feet (6.1 meters) and can be elevated to an angle of about eighty degrees with respect to the machine.
In a typical machine the elevation and lowering of the boom is accomplished by a hydraulic boom lift cylinder. A control lever is moved by the operator to effect a lowering or raising of the boom. In a typical machine the boom elevation control circuit is a closed centered, load sensing, pressure compensated circuit, therefore the boom lift cylinder velocity remains constant at all lever positions for a given engine speed. In such a system, however, the geometry of the boom to the chassis of the machine and the boom lift cylinder causes the angular velocity of the boom to vary widely depending on the angle of the boom to the chassis. The relationship causes the angular velocity to increase as the angle of the boom to the chassis increases. The change in angular velocity with boom angle makes it very difficult for the operator to precisely control the distant end of the boom as the boom angle increases. This becomes especially difficult as the boom is also extended.
Thus, it would be desirable to provide a control wherein the angular velocity of the boom is constant, for a given lever position and engine speed, over a range of boom angles.
The present invention is directed to overcome one or more of the problems as set forth above.
In one aspect of this invention, a method for maintaining a constant angular velocity for a boom of a machine is disclosed. This method includes the steps of pre-selecting a desired angular velocity for a boom of a machine, forming a triangle, the first leg comprising a fixed distance A between a pivot point of the boom to the machine and an attachment point of a boom lift cylinder to the boom, the second leg comprising a fixed distance B between the pivot point of the boom to the machine and an attachment point of the boom lift cylinder to the machine, and the third leg comprising a variable distance C between the attachment point of the boom lift cylinder to the boom and the attachment point of the boom lift cylinder to the machine, distance C varying as the boom lift cylinder extends and retracts to lift and lower the boom, determining the length of distances A, B and C at a first point in time, determining at the first point in time the value of the sine of an angle xcex8 formed by the intersection of the first leg and the second leg, calculating at the first point in time a boom gain value by dividing the product of A, B, and the sine of xcex8 by C, calculating a desired boom lift cylinder velocity at the first point in time by taking the product of the boom gain at the first point in time and the pre-selected desired angular velocity, adjusting an actual boom lift cylinder velocity to equal the desired boom lift cylinder velocity, thereby producing an actual angular velocity of the boom that equals the pre-selected desired angular velocity, and repeating the step of determining the length of distances A, B and C at a first point in time through the step of adjusting an actual boom lift cylinder velocity to equal the desired boom lift cylinder velocity, thereby producing an actual angular velocity of the boom that equals the pre-selected desired angular velocity at a second point in time wherein the length of C and therefore the value of the sine of angle xcex8 are different at the second point in time from the first point in time.
In another aspect of the invention an angular velocity control for a boom of a machine is disclosed. This control includes a boom pivotally attached to a pivot point on a machine, an operator control lever, movement of the control lever from a reference position to a first position different from the reference position generating a first angular velocity signal, the first angular velocity signal associated with a desired angular velocity of the boom, a hydraulic boom lift cylinder having a first end attached to the boom at a cylinder attachment point spaced a distance A from the pivot point, a second end attached to the machine at a point spaced a distance B from the pivot point, and a distance C between the first and the second ends, extension and retraction of the cylinder pivoting the boom about the pivot point, a triangle having as apexes the pivot point, the first end and the second end, and an angle xcex8 within the triangle having the pivot point as an apex, a sensor, the sensor detecting one of the distance C or the angle xcex8, a calculator, the calculator calculating the other of the distance C or the angle xcex8 based on the distance A, the distance B and the sensed one of the distance C or the angle xcex8, the calculator calculating a boom gain by dividing the product of the distance A, the distance B and a sine of the angle xcex8 by the distance C, the calculator detecting the first angular velocity signal and calculating a desired cylinder velocity equal to the product of the desired angular velocity and the boom gain, and the calculator generating a control signal associated with the desired cylinder velocity, and an electrohydraulic control module, the control module detecting the control signal and actuating an electrohydraulic valve associated with the cylinder, actuation of the valve flowing a hydraulic fluid into or out of the cylinder at a flow rate based on the control signal, the flow rate producing an actual cylinder velocity of the cylinder equal to the desired cylinder velocity.